Molecule separator

ABSTRACT

Molecule separator according to the jet principle comprising at least one separation stage with an evacuation chamber, connected to a pump provided with two coaxially arranged nozzles for the gas phase subject to separation, one of said nozzles being axially displaceable, said molecule separator further comprising control means in order that the distance between said nozzles can be varied from outside said separator during separation.

United States Patent 9 Ryhage Apr. 16, 1974 f MOLECULE SEPARATOR [75] inventor: Erik Ragnar Ryhage, Stockholm, prlma'y Exammer chafles Hart Sweden [73] Assignee: LKB-Produkter AB, Bromma,

Sweden [57] ABSTRACT 22 Filed: Nov. 6, 1972 Molecule separator according to the et principle com- PP N05 303,878 prising at least one separation stage with an evacuation chamber, connected to a pump provided with two [30] Foreign Application Priority Data coaxially arranged nozzles for the gas phase subject to Nov 10 1971 Sweden 1 4362/71 separation, one of said nozzles being axially displaceable, said molecule separator further comprising control means in order that the distance between said [52] [1.8. CI. 55/197, 55/17 i 51 Int. Cl B0ld 53/02 g zf izgx fmm (made separam [58] Field of Search 55/15, 17,67, 197,277, g p

[56] References Cited r 4 Claims, 2 Drawlng Flgures 3,678,656 7/1972 Brunner et al 55/197 r/ l z/ z I r l l 7' v v ///s/ I a 11. /1// I a I r I /.v v l z 2 8 j-' 4' I .l/ I Ks PATENTEUAPRI 51914 SHEET 2 or 2 MOLECULE SEPARATOR The present invention relates to a molecule separator working according to the jet principle and-comprising at least one separator step consisting of an evacuation chamber connected to a pump, to which chamber mol ecules in gas phase are supplied through a jet nozzle, an output nozzle being arranged coaxialto the jet nozzle in order that molecules ,with great molecular mass are passing to a greater extent through the output nozzle than are molecules with less molecular mass.

In a combination instrument, comprising a gas chromatograph, the output of whichis connected to the ion source of a mass spectrometer and the purpose of which is the analysis of organic chemical substances, the mass spectrometer is normally operated under essentially lower pressure than the gas chromatograph. Consequently a pressure reduction must be accomplished between these components, which for example is achieved by means of a molecule separator, working accordingto the jet principle and connected between the output of the gas chromatograph and the ion source of the mass spectrometer. In this type of separator, described'for example in the German Pat. specification No. 1,052,955, a pressure reduction ,is achieved by forcing the gas flow from the gas chromatograph, consisting of sample and carrier gas with high velocity, to pass through an input nozzle to a chamber with reduced pressure, an' output nozzle being arranged coaxial to the input nozzle. In that way the pressure is being reduced at the same time as an enrichment of sample in relation to the carrier gas is achieved. The separation then usually is carried out in at least two stages.

In the first stage in which the chamber is connected to an ordinary mechanical prevacuum pump, the pressure is reduced from atmospheric. pressure to 0,l-0,3 mm Hg. In the second stage, connected to an oil diffusion pump, the pressure is lowered to about 0,001 mm Hg. About 99 percent of the carrier gas is separated totally, while at least 50-75% of the sample remains, depending on the nature of the sample.

Such a device has been described by the inventor in Analytical Chemistry, Vol. 36, No. 4, April, 1964, pages 759-764.

It is often desired, however, to carry out the analysis by means of a gas chromatograph column of capillary type, or with a reduced flow in the column. The pressure reduction, accomplished in the molecule separator, would in these cases result in too low a pressure in the mass spectrometer.

In order to compensate for thelow flow in the gas chromatograph it is hitherto proceeded in that way that an extra carrier gas flow is supplied between the gas chromatograph and the molecular separator. See for instance the German Pat. No. 1,096,875. This method brings about unreliability in the analysis in that way that the sample is diluted by carrier gas in great excess, leading to an increased carrier gas pressure inthe mass spectrometer tube. This will lead to a falling off of the resolution of the mass spectrometer.

Another method, which is particularly applied at the use of capillary columns, is that the action of the first separator is completely eliminated in that way that a tube, usually of silver, is attached between the jet nozzle and the'output nozzle, in that way that the gas flow is conducted directly to the second separator stage. This method however involves a heavy encroachment into the apparatus and is only suitable for definitive reconstruction of the apparatus for a capillary column.

Generally, however, it is desirable to change between use of a normalcolumn and use of a capillary column.

It is also in some instances desirable to'make possible a greater flow in the gas chromatograph column than normal, by increasing the distance between the nozzles of the molecule separator.

The purpose of the present invention is to provide a device by means of which the distance between the nozzles of the molecule separator can be varied and by means of which the nozzles also can be completely pushed together.

. The purpose of the present ivention is also to provide a device by means of which the distance between the nozzles of the molecule separatorcan be varied during separation, controlled from outside the combination instrument.

The optimal nozzle distance varies according to the magnitude of the supplied gas flow as well as according to its composition. The possibility of adjusting the nozzle distance according to the output-measurement signal during separation highly improves the possibility to achieve an optimal nozzle distance.

Thus, another purpose of the present invention is to make possible to maintain in the ion source of the mass spectrometer a suitable pressure independent of the flow in the gas chromatograph.

Another advantage of the present invention is that the costs of manufacture could be lowered, because the possibilities of accurate readjustment of the nozzle distance' in the completed combination instrument disminishes the demands on the accuracy of manufacture regarding the nozzle distance in the molecule separator.

The characteristics of the invention are obvious from the claims following the specification.

The invention will now be further explained with reference to the attached drawing, in which FIG. 1 and FIG. 2 are showing two embodiments of I nozzle of the separator stage is denoted by 5. 6 denotes a flange which is screwed onto the separator stage 1 by means of screws, not shown in the FIG. 7 and 8 denotes two metal membranes, joined by soldering to the tube 3, and being part of the system of sealings between that gas, the molecules of which are subject to separation, and the surrounding atmosphere. The remaining elements of this sealing system are a ring 9 and silver sealings 10 and 11. The axial displacement of the tube 3 is achieved by means of an eccentric 12 by turning of an axle 13. The eccentric l2 acts on a casing 14, which is mechanically connected to the tube 3 by a screw 15.

The device according to the invention works in the following way:

When it is desired to change the distance between the nozzles of the separator stage, the axle 13 is turned. Then the eccentric 12 will bring the casing 14 to move in axial direction. Thereby the casing 14 take the tube 3 with it, provided that the screw 15 is tightened. The tube 3 is carried by the metal membranes 7 and 8, which ones allow a sufficient axial clearance of the tube 3. The sealing between that gas phase, the molecules of which is subject to separation and which is flowing through the supply line 4 and further through the tube 3, and the surrounding atmosphere, is accomplished in that way that the ring 9 is pressed towards the separator stage 1 by the flange 6, in that way that the sharp edges of the ring 9 are pressing onto the metal membranes 7 and 8 which then are tightening towards the silver seals 10 and 11.

At a coarse adjustment of the nozzle distance the screw is loosened and the casing 14 is displaced relative to the tube 3.

The embodyment of the device according to the present invention, shown in FIG. 2, differs from the embodiment described above mainly in the sealing device. In FIG. 2 l6 denotes a partly slotted casing, clasping the tube 3. l7 denotes a teflon sealing, 18 a silver sealmg.

The displacement device according to this embodiment works in similar manner as that one described above. At turning of the axle 13 the eccentric 12 makes the casing 16 to move in axial direction. The casing 16 then takes the tube 3 with it, due to the friction coupling present between the casing and the tube. The sealing between that gas phase, the molecules of which is subject to separation, and the surrounding atmosphere is accomplished by the teflon sealing l7 and the silver sealing 18.

In the devices shown by way of example in the drawings the adjustment of the distance between the nozzles of the separator stage is achieved in that way that the jet nozzle is axially displaceable. A device with an axially displaceable output nozzle of course fulfills the same purpose and should be part of the invention. A separator according to the jet principle could be made in one or several stages, and is generally made in two stages. One or more stages then can be provided with the device according to the invention.

In the embodiments of the invention, shown by way of example in the drawings, the control means, which is displacing the axially displaceable tube, consists of an axle with an eccentric in one end of it. Control means, designed in other ways, are also conceivable within the scope of the invention. For instance the control means could consist of a axially displaceable rod, the movement of which is transferred to axial movement of the nozzle. This rod can be parallel to the direction of the tube 3 or form an angle, for instance to this direction. The design of the sealings should not be restricted to what is described herein.

I claim:

1. Molecule separator working according to the jet principle, comprising at least one separator stage comprising an evacuation chamber, connected to a pump, to which evacuation chamber molecules in gas phase are supplied via a jet nozzle, an output nozzle being arranged coaxially to said jet nozzle in order that molecules with great molecular mass will pass through said output nozzle to a greater extent than will molecules of small molecular mass, said molecule separator further comprising an axially displaceable tube, that end of which, turned towards said evacuation chamber, forms one of said nozzles of the separator, and further a control means, which is performing the displacement in axial direction of said tube, and sealings between that gas phase, the molecules of which are subject to separation, and the atmosphere at the outer end of the control means, in order that the distance between the jet nozzle and the output nozzle can be varied from outside said separator during separation.

2. Molecule separator according to claim 1 in which said control means comprises an axle, perpendicular to said axially displaceable tube, said axle giving, when turned, the axial displacement of said tube by means of an eccentric.

3. Molecule separator according to claim 2 in which said eccentric is acting on a casing which is surrounidng said tube and is transferring its axial displacement to the tube by means of a mechanical coupling.

4. Molecule separator according to claim 3 in which said casing and that part of said tube which is surrounded by said casing is situated with respect to said sealings so as to be delimited towards that gas phase,

the molecules of which are subject to separation. 

1. Molecule separator working according to the jet principle, comprising at least one separator stage comprising an evacuation chamber, connected to a pump, to which evacuation chamber molecules in gas phase are supplied via a jet nozzle, an output nozzle being arranged coaxially to said jet nozzle in order that molecules with great molecular mass will pass through said output nozzle to a greater extent than will molecules of small molecular mass, said molecule separator further comprising an axially displaceable tube, that end of which, turned towards said evacuation chamber, forms one of said nozzles of the separator, and further a control means, which is performing the displacement in axial direction of said tube, and sealings between that gas phase, the molecules of which are subject to separation, and the atmosphere at the outer end of the control means, in order that the distance between the jet nozzle and the output nozzle can be varied from outside said separator during separation.
 2. Molecule separator according to claim 1 in which said control means comprises an axle, perpendicular to said axially displaceable tube, said axle giving, when turned, the axial displacement of said tube by means of an eccentric.
 3. Molecule separator according to claim 2 in which said eccentric is acting on a casing which is surrounidng said tube and is transferring its axial displacement to the tube by means of a mechanical coupling.
 4. Molecule separator according to claim 3 in which said casing and that part of said tube which is surrounded by said casing is situated with respect to said sealings so as to be delimited towards that gas phase, the mOlecules of which are subject to separation. 